Video disc record having spirally aligned sync storage locations

ABSTRACT

Video disc record is provided with a spiral information track containing recorded representations of composite video signals. The information representations occupying the length of each convolution of the spiral depart slightly from an integral number of field intervals by a fixed amount. The departure amount is such that the information content per spiral convolution corresponds to a given integral number of line intervals plus a predetermined fraction of a line interval (other than one-half). Synchronizing information locations in successive convolutions are thus staggered in a spiral manner. Recording apparatus for forming such a record includes apparatus for maintaining the rate of rotation of a recording turntable substantially constant at a rate which differs from an integral submultiple of the field rate of the composite video signals supplied to the recorder by an appropriate small amount.

The present invention relates generally to novel video disc records andnovel recording/playback apparatus and methods therefor, andparticularly to a novel form of video disc record wherein synchronizinginformation locations in successive convolutions of a spiral informationtrack are staggered in a spiral manner, to novel recording apparatus andmethods for use in forming a record of such a "spiral sync"configuration, and to novel playback apparatus and methods foradvantageous use with such a record.

In U.S. Pat. No. 3,842,194, issued on Oct. 15, 1974 to Jon K. Clemens,video disc playback systems of a variable capacitance form aredisclosed. In an arrangement therein disclosed, an information trackincorporates geometric variations in the bottom of a spiral groove in adisc, the surface of which comprises conductive material covered with athin coating of dielectric material. Variations in the capacitancepresented between a conductive electrode on a tracking stylus and theconductive material of the disc occur as the disc is rotated by asupporting turntable; the capacitance variations are sensed to recoverthe recorded information.

In one particularly successful format employed for the groove bottominformation track in practice of the Clemens invention, depressed areasextending across the groove bottom alternate with non-depressed areas,with the frequency of alternation varying with the amplitude of videosignals subject to recording. The form of the recorded signal is thus acarrier frequency modulated in accordance with video signals. In anadvantageous arrangement for recording such information on a pre-groovedvideo disc master, an electron beam subject to intensity modulation inaccordance with FM picture carrier signals, impinges upon electron beamsensitive material in the master disc groove bottom, so that subsequentdevelopment leaves the desired relief pattern in the groove bottom. Thecopending application of Loren B. Johnston, Ser. No. 335,024, filed Feb.23, 1973 and entitled "Electron beam Recording In Thick Materials", nowU.S. Pat. No. 3,943,302, contains a description of advantageousrecording techniques that may be employed in such relief patterndevelopment. The copending application of R. W. Jebens, et al., Ser. No.349,775, filed on Apr. 10, 1973 and entitled "Precision TurntableRotation In A Vacuum Atmosphere" now U.S. Pat. No. 3,943,275, describessuitable apparatus for achieving precise control of the rotation of adisc-supporting turntable in a recording system of the above-describedelectron beam recording type.

In an illustrative application of the principles of the presentinvention, the rotation rate of a recording master disc in an electronbeam recorder is controlled, by apparatus of the general form describedin said Jebens, et al application, so as to differ slightly from asubharmonic of the field rate of the video signal information content ofthe recording signal input supplied to the recorder. The degree ofdifference is precisely controlled so that the video information contentper convolution of the spiral recorded information track corresponds toa given integral number of line intervals plus a predetermined fractionof a line interval, with the predetermined fraction desirably beingother than 1/2. In the developed master, and in replica discs derivedtherefrom (for example, by replication methods of the type described insaid Clemens patent), horizontal synchronizing information storagelocations in successive convolutions of the spiral information track arestaggered in a spiral manner. In playback of a disc having the aforesaidspiral sync format, separation of horizontal sync signals from thecomposite video signals recovered from the disc provides recurringinformation which is indicative, by way of its phasing, of theoccurrence of a departure from the normal progression of traversals ofsuccessive track convolutions by the player's signal pickup. With theaforementioned line interval fraction choice of other than one-half, thedirection of such departure is indicated moreover. As explained morefully in a copending application Ser. No. 522,817, of Thomas W. Burrus,filed concurrently herewith and entitled "Locked Groove Detection AndCorrection In Video Disc Playback Apparatus", and now issued as U.S.Pat. No. 3,963,860, use may be made of such occurrence indication toautomatically detect and correct and undesired mode of player operationinvolving repetitive replays of information recorded in givenconvolutions of the spiral information track.

In an illustrative emmbodiment of the record aspects of the presentinvention, the video information content per convolution of the spiralinformation track corresponds to 2097.9 line intervals (or 2.1 lineintervals less than eight full field intervals, for a 525line-per-frame-interval picture). In an illustrative embodiment of theplayer aspects of the present invention, a video disc player is providedwith a turntable rotational drive system of a power line synchronousform (illustratively incorporating a synchronous motor) to effectrotation of the turntable at a rate corresponding to an integralsubmultiple of the power line frequency, with the specific example being7.5 rps rotation rate for a power line frequency of 60 Hz. The playercooperates with a spiral sync disc of the above-specified 2097.9lines-per-convolution standard to recover composite video signals with aU.S. color broadcast standard field rate of 59.94 fields per second (notharmonically related to the turntable rotation rate). Horizontal syncsignals, separated from the composite video signals recovered from therecord, indicate by a sustained phase advance a shift of signal pickupto an outwardly adjacent track convolution, in contrast with a sustainedphase lag indication of a shift of signal pickup to an inwardly adjacenttrack convolution.

Objects and advantages of the present invention will be readilyrecognized by those skilled in the art upon a reading of the followingdetailed description, and an inspection of the accompanying drawings inwhich:

FIG. 1 illustrates partially by block diagram representation, video discrecording apparatus pursuant to a specific embodiment of recordingaspects of the present invention.

FIG. 2 illustrates diagrammatically the disposition of horizontalsynchronizing information in successive convolutions of a spiralinformation track of a video disc record pursuant to a specificembodiment of record aspects of the present invention; and

FIG. 3 illustrates, partially by block diagram representation, videodisc playback apparatus pursuant to a specific embodiment of playeraspects of the present invention.

In the arrangement of FIG. 1, an audio signal source 20 provides soundinformation appropriate for recording with the color picture informationprovided by a composite color video signal source 10, the latterproviding composite color video signals having a field repetition rateof f_(v).

The output of audio signal source 20 is applied to a sound carrierfrequency modulator 22 to develop a first FM signal comprising carrierfrequency waves varying in frequency about a relatively low centerfrequency in accordance with the amplitude of the source 20 output. Asecond FM signal is developed by the picture carrier frequency modulator12 in response to the output of the composite color video signal source10. The carrier frequency deviation range for modulator 12 occupies arelatively high frequency band, with the output of source 10illustratively poled so that transitions from black toward white causean increase in the picture carrier frequency.

Duty cycle modulation of the picture carrier wave output of modulator 12is effected in accordance with the FM sound carrier wave output ofmodulator 22 by a duty cycle modulator 24, comprising an adder 26 forsumming the two FM signals and a limiter 28 for double clipping theresultant sum. Reference may be made to my copending application, Ser.No. 441,069, filed on Feb. 11, 1974, now U.S. Pat. No. 3,911,476 for amore detailed discussion of the duty cycle modulation process hereemployed. The magnitude of the sound modulator output supplied to adder26 is chosen so that its peak-to-peak amplitude is small relative to thepeak-to-peak amplitude of the output of the picture carrier modulator12, and double clipping level in limiter 28 are set with a spacingappreciably smaller than the peak-to-peak swing of the sound modulatoroutput.

The output of the duty cycle modulator 24, appearing at the limiteroutput terminal R, serves as the recording signal input to an electronbeam recorder 30 of the scanning electron microscope (SEM) typegenerally described in the above-mentioned Clemens patent. In theelectron beam recorder, a scanning electron microscope 31 directs a beamof electrons upon the curved groove bottom of a pre-grooved recordingmaster disc 70, the curved groove bottom surface comprising electronbeam sensitive material. The disc 70 is supported by a turntable 32which is subject to (a) rotational motion imparted by a turntablerotational drive mechanism 34, and (b) translational motion imparted bya turntable translational drive mechanism 35. The rotational andtranslational drives are interrelated in such manner that the electronbeam path is intercepted in turn by successive regions along the lengthof successive convolutions of the disc's spiral groove in a regularinward progression toward the disc center. Reference may be made to thecopending application of Robert W. Jebens, et al. Ser. No. 349,775,filed on Apr. 10, 1973 and entitled "Precision Turntable Rotation In AVacuum Atmosphere", now U.S. Pat. No. 3,943,275, for an illustration ofsuitable apparatus for effecting the requisite controlled motion of theturntable 32.

Illustratively, the electron beam of SEM 31 is unblanked for theduration of each positive swing of the clipped signal at terminal R, andblanked for the duration of each negative swing of the clipped signal.The sweep rate for the SEM beam is considerably higher than the highestfrequency of the picture carrier deviation range, while the beam sweepamplitude and unblanked beam intensity are substantially constant. Asthe disc record 70 rotates at a constant speed, a pattern of successiveexposed and unexposed regions is produced along the length of thegroove, with the lengths thereof (along the groove) determined by therespective swing durations of the recording signal input. Assuming, forexample, that the master disc groove surface material is a positiveresist, a subsequent development step will leave a pattern ofalternating depressed and (relatively) non-depressed regions in thegroove bottom corresponding to the pattern of exposed and unexposedregions, respectively.

Pursuant to the principles of the present invention, the speed ofrotation of the disc 70 provided by the turntable rotational drivemechanism 34 is maintained substantially constant at a rotation rate off_(R), where f_(R) differs slightly from an integral sub-multiple off_(V) by a controlled amount. The controlled amount is desirably suchthat the time required for SEM beam path interception by the groovebottom regions of a full convolution of the spiral groove of disc 70corresponds to the time occupied by an integral number of line intervalsplus a predetermined fraction, other than one-half, of a line interval,at the line repetition rate of the signals provided by source 10.

An illustrative arrangement for effecting control of the disc rotationrate, as shown in FIG. 1, employs a tachometer disc 36 carrying suitableindicia, illustratively comprising a selected number of regularly spacedmarkings 37 on its periphery. The disc 36 is mounted for rotation on theturntable shaft 33 to which turntable 32 is secured for rotation. Atachometer pickup 40, located adjacent the periphery of the rotatingdisc 36, responds to the passage of each disc marking 37 by developingan electrical pulse. Illustratively, the pickup 40 may comprise anoptical sensor responsive to differences in light reflectance of markedand unmarked regions of disc 36 periphery passing through the sensor'slimited field of view.

The signals developed by pickup 40 are amplified by amplifier 42 andthen supplied to a frequency divider 44. A second frequency divider 61receives the output of a reference crystal controlled oscillator 60. Theoutputs of the two frequency dividers are supplied to a frequencycomparator 50. The frequency comparator 50 develops a control voltageoutput having an amplitude and polarity respectively indicative of themagnitude and sense of the departure, if any, of the frequency of theoutput of divider 44 from substantial frequency identity with thereference frequency of the output of divider 61. The output of frequencycomparator 50 is amplified by control voltage amplifier 52 for deliveryto a control terminal C of the turntable rotational drive mechanism 34.

Illustratively, the turntable rotational drive mechanism is of a fluidpropulsion form, as described in detail in the aforesaid Jebens, et al.application. With such form of drive mechanism, the control voltageinformation available at terminal C may be applied to a suitable fluidcontrol valve so as to effect the desired turntable speed regulation viacontrol of the intensity of the propelling fluid stream (as illustratedin the aforementioned Jebens, et al. application).

In an illustrative application of the principles of the presentinvention, operating parameters for the FIG. 1 recording apparatus arechosen so that the recorded information content per convolution of thespiral groove of disc 70 corresponds substantially to 2097.9 lineintervals, where the format of the video signals is such that a frame oftwo interlaced fields thereof comprises 525 line intervals. In thisillustrative instance, the recorded information content duration pergroove convolution differs from an integral number of field intervals bya small amount; i.e., being less than eight field intervals by an amountcorresponding to 2.1 line intervals.

FIG. 2 presents a diagrammatic showing of the recorded informationalignment that results in successive groove convolutions of disc 70 (andin replica discs derived therefrom) when the aforesaid illustrativechoice of recording parameters is made. In the FIG. 2 diagram,vertically disposed lines R_(o) and R₁ represent respective radii of thedisc record, while horizontally disposed lines c₁, c₂ and c₃ representaligned segments of the information track in three successiveconvolutions of the disc's sprial groove, with track segment c₁ lying inthe outermost of the illustrated trio of convolutions. The portion ofeach track segment lying between R_(o) and R₁ is of sufficient arcuatedistance to encompass a video signal portion of a duration correspondingto six line intervals.

Illustratively, the six line portion of video signal information fallingbetween radii R_(o) and R₁ along convolution c₁ corresponds tointermediate lines 89, 91, 93, 95, 97 and 99 of an odd-line field. Thetrack regions along this convolution (c₁) occupied by the recordedpicture information for said lines of the odd-line field are designatedgenerally by references L89, L91, L93, L95, L97 and L99 in FIG. 2. (Itmay be noted that primed references are used for correspondingdesignation of picture information regions in convolution c₂, and doubleprimed references are used therefor in convolution c₃.) The track regionoccupied by recorded information representative of the horizontal syncpulse preceding each of the designated lines is bracketed by shortvertical lines. The beginning of the recording location for thehorizontal sync pulse preceding line 89 of the field occupying theillustrated segment of convolution c₁ is aligned with the radius R_(o).

In the inwardly adjacent convolution c₂ of the information track, thetrack regions in the R_(o) -R₁ segment are again representative ofintermediate lines in an odd-line field, but there is a slippage fromradial alignment of information concerning corresponding lines. Thebeginning of the recording location for the horizontal sync pulsepreceding line 89 of the field occupying the illustrated segment ofconvolution c₂ is shifted from R_(o) by an arcuate distancecorresponding to two and one-tenth line intervals (2.1 h). The beginningof the recording location for the horizontal sync pulse preceding line89 of the field occupying the illustrated segment of convolution c₃ isshifted from the c₂ location in the same direction by the same (2.1h)amount. The shift is in a direction opposite to the direction of groovemotion (designated by arrow d in FIG. 2) relative to the recording beampath which occurs when disc 70 is rotated during the operation of theFIG. 2 apparatus. This is also the intended direction of groove motionrelative to signal pickup for playback of a replica of disc 70.

As a consequence of the above-discussed degree of slippage from radialalignment in successive convolutions of information concerningccorresponding lines, there is a net slippage from radial alignment insuccessive convolutions of horizontal sync pulse recording locations ofa magnitude corresponding to one-tenth of a line interval (0.1H). Thus,for example, the beginning of the recording location for the horizontalsync pulse preceding line 85 of the field occupying the illustratedsegment of convolution c₂ is shifted from R_(o) by an arcuate distanceof 0.1H, while the beginning of the recording location for thehorizontal sync pulse preceding line 81 of the field occupying theillustrated segment of convolution c₃ is shifted from R_(o) by anarcuate distance of 0.2h. These shifts are again in direction oppositeto the groove motion direction d.

Accordingly, the horizontal sync pulse recording locations in successiveconvolutions of the spiral information track of recorded disc 70 and itsreplicas are not radially aligned, but rather are staggered,convolution-to-convolution, in a manner establishing a spiral alignment.

FIG. 3 illustrates record playback apparatus that may be advantageouslyemployed in recovery of signals from a video disc record 70', replicatedfrom a master recording disc 70 of the FIG. 2 form (as by use of thereplication methods discussed in the aforesaid Clemens patent), pursuantto an illustrative embodiment of record player aspects of the presentinvention.

In the player arrangement of FIG. 3, the replica disc 70' is supportedby a turntable 105. The turntable 105 is rotated at a substantiallyconstant playback rotation rate by a suitable rotational drive mechanismin which the motive power is supplied by a synchronous motor 103,energized by alternating current supplied by an alternating currentsource 101. Illustratively, source 101 is the house current supply(i.e., mains supply) for the record player's site, and the frequency ofthe energizing current f_(p) is the power line frequency (i.e. mainsfrequency) provided for local current distribution. The rotation ratef_(t) established for disc 70' by the rotational drive provided bysynchronous motor 103 corresponds to an integral submultiple of f_(p).

a signal pickup 109 is provided for traversing the successiveconvolutions of the spiral information track of the rotating disc record70' to recover the recorded signal information. Illustratively, thesignal pickup 109 is a stylus with a groove-entering tip of the generalform described in the aforesaid Clemens patent, and incorporates anelectrode which cooperates with material of the disc record 70' toestablish capacitance variations representative of the recorded signalinformation as the groove bottom geometry variations constituting therecorded information track pass beneath the stylus. Pickup circuits 110,which may illustratively be of the form disclosed in th copending U.S.patent application of D. J. Carlson, et al., Ser. No. 451,103, filedMar. 14, 1974, now U.S. Pat. No. 3,872,240, convert the capacitancevariations to electrical signal variations (of a form generallycorresponding to that of the recording signal provided at terminal R inthe recording apparatus of FIG. 1).

The signal output of pickup circuits 110 is supplied to a pair ofbandpass filters 121, 131. Bandpass filter 121 is provided with apassband encompassing the relatively low frequency sound carrierdeviation range and appropriate adjacent sideband regions. The signalportion selectively passed by filter 121 is applied via a limiter 123 toa sound carrier FM demodulator 125. The recorded FM sound carrier isdemodulated to recover audio signals which appear at the demodulatoroutput terminal A. The audio signals at terminal A are supplied toappropriate audio signal utilization circuits 127.

Bandpass filter 131 is provided with a passband encompassing therelatively high frequency picture carrier deviation range andappropriate adjacent sideband regions. The signal portion selectivelypassed by filter 131 is applied via a limiter 133 to a picture carrierFM demodulator 135. The recorded FM picture carrier is demodulated torecover composite color video signals which appear at demodulator outputterminal v. The composite color video signals at terminal V are suppliedto appropriate composite color video signal utilization circuits 137.

Illustratively, the utilization circuits 127, 137 may comprise apparatusfor processing the respective demodulator outputs to a form suitable forapplication to the antenna terminals of a conventional color televisionreceiver, so as to permit picture display and sound reproduction by thereceiver. Reference may be made to the copending U.S. patent applicationof John G. Amery, Ser. No. 506,446, filed Sept. 16, 1974, now U.S. Pat.No. 3,938,179, for an illustrative showing of suitable apparatus forprocessing composite color video signals from a form appropriate forrecording to a form appropriate for receiver use. Reference may also bemade to U.S. Pat. No. 3,775,554, issued to Bernard Hjortzberg on Nov.27, 1973, for a disclosure of transmitter apparatus suitable for use inconverting the processed video and audio signals to a modulated RFcarrier form suitable for antenna application purposes.

Pursuant to an aspect of the present invention, the recovered compositecolor video signals appear at terminal V with a field repetition ratef_(v) _(') which is not harmonically related to the turntable rotationrate f_(t). That is, the nominal turntable rotation rate (f_(t) 9differs from an integral submultiple of the field rate (f_(v) _(')) ofthe recovered video signal information by a selected small amount.

An illustrative value for the turntable rotation rate (f_(t)) is 7.5 rps(or 450 rpm), which results in the recovery of video signals fromreplica disc record 70' (when the latter has the specific form discussedin connection with FIG. 2) with a field repetition rate of approximately59.94 fields per second (corresponding, for example, to the U.S. colorbroadcast field rate standard). The illustrative value of 7.5 rps forf_(t) corresponds to an integral submultiple of a conventional powerline frequency (60 Hz.) employed, for example, in the United States.

It will be seen that in the illustrative example given above, one isenabled through use of the present invention to employ a power linesynchronous drive system for the playback turntable in the player'sdevelopment of composite color video signals with a field rateasynchronously related to the power line frequency. Reference may bemade to the copending U.S. patent application Ser. No. 504,486, filed onSept. 10, 1974 for Robert J. Hammond, et al., now U.S. Pat. No.3,912,283, for an illustration of relatively inexpensive apparatus thatmay be employed to effect rotational drive of turntable 105 in a powerline frequency synchronous manner.

Illustratively, the composite color video signal processing apparatusincorporated in utilization circuits 137 includes a suitable syncseparator circuit for separating horizontal synchronizing informationfrom the composite color video signals appearing at terminal V, anddeveloping a train of horizontal sync pulses at terminal H of theutilization circuits 137. One illustrative form of sync separatorapparatus is shown, for example, in the copending U.S. patentapplication of Charles D. Boltz, Jr., Ser. No. 402,081, filed on Oct. 1,1973, now U.S. Pat. No. 3,914,542.

By virtue of the aforementioned spiral alignment of sync pulse recordinglocations in successive convolutions of the information track of discrecord 70', the pulse train provided at terminal H serves to indicate bya shift in phasing of the sync pulses a departure from the normalprogression of track convolution traversals by signal pickup 109. Thatis, for example, if during the traversal of convolution c₂, the signalpickup 109 jumps to the inwardly adjacent convolution c₃, a shift of thesync pulses at terminal H to a new phase location, lagging the phaselocation that would be occupied if normal traversal of convolution c₂had continued, occurs. An opposite shift to a leading phase locationresults if the pickup jump is oppositely directed to the outwardlyadjacent convolution c₁. Reference may be made to the copending U.S.patent application Ser. No. 522,817, of Thomas W. Burrus, concurrentlyfiled herewith an entitled "Locked Groove Detection And Correction InVideo Disc Playback Apparatus", and now issued as U.S. Pat. No.3,963,860, for an illustration of apparatus that may advantageouslyemploy the noted indication provided by the signals at terminal H.

Where "real time" recording is employed in the recording apparatus,illustrative values for recording turntable rotation rate (f_(R)) andsource field rate (f_(V)) of 7.5 rps and 59.94 Hz., respectively, willprovide a record 70 of the specific form discussed in connection withFIG. 2. However, where required, for example by limitations on recordingbeam intensity and/or sensitivity of the electron beam sensitivematerial employed in the groove of disc 70, a slower-than-real-timerecording mode may be employed, with the recording turntable rotationrate a fraction (e.g., 1/21) of the intended playback disc rotationrate. In such an instance, the recording signal parameters are subjectto division by the involved time expansion factor (e.g., 21).

In an illustrative application of the principles of the presentinvention to the aforesaid slower-than-real-time recording mode, wheref_(v) corresponded to 59.94 Hz. divided by 21, the recording turntablerotation rate (f_(p)) was maintained at 7.5 rps divided by 21. Suchmaintenance was effected using: a tachometer disc 36 with 10,800markings (37) regularly spaced about its periphery; a referencefrequency for the output of oscillator 60 of 1,000,000 Hz.; frequencydivision of the output of amplifier 42 by a factor of 23 in frequencydivider 44; and frequency division of the output of oscillator 60 by afactor of 5,963 in frequency divider 61.

While the present invention has been specifically described above interms of application to a video disc system of the capacitance typedescribed in the previously mentioned Clemens patent, it should beappreciated that the principles of the present invention may also beemployed to advantage in video disc systems of other types (e.g.,optical disc systems).

What is claimed is:
 1. A composite video signal record comprising:a dischaving a surface bearing a spiral information track; said informationtrack containing recorded representations of successive frames ofinterlaced fields of composite video signals inclusive of horizontalsync signals recurring at a given line repetition rate, with each ofsaid frames containing an odd integral number of line intervals; saidsignal representations being distributed along the convolutions of saidspiral information track in such manner that each convolution of saidspiral information track contains composite video signals occupying aneven integral number of frame intervals less the sum of a small integralnumber of line intervals and a predetermined fraction of a lineinterval, several times smaller than a half-line interval.
 2. A recordin accordance with claim 1 wherein said predetermined fraction isone-tenth, whereby locations representative of recorded horizontal syncsignals in any given track convolution deviate from radial alignmentwith locations representative of recorded horizontal sync signals in animmediately adjacent track convolution by an arcuate distance occupiedby one-tenth of a line interval of recorded composite video signalinformation having said line repetition rate.
 3. A record in accordancewith claim 1 wherein each of said successive frames comprises a pair ofinterlaced fields, wherein said integral number of frame intervals isfour, and wherein said small integral number of line intervals is two.4. A composite video signal record comprising:a disc having a surfacebearing a spiral information track; said information track containingrepresentations of recorded composite video signals inclusive ofregularly recurring horizontal sync signals; said signal representationsbeing distributed along the convolutions of said spiral informationtrack in such manner that (1) recorded horizontal sync signal locationsin successive convolutions of said track are spirally aligned, and (2)the arcuate distance between an edge of any of said recorded horizontalsync signal locations and the corresponding edge of the nearest recordedhorizontal sync signal location in an adjoining convolution of saidspiral information track corresponds to that occupied by a predeterminedportion of a line interval of recorded composite video signalinformation, said predetermined portion being several times smaller thana half-line interval.
 5. A composite video signal record comprising:adisc having a spiral groove in a major surface thereof; said spiralgroove containing an information track comprising geometric variationsalong the bottom of said groove representative of recorded compositevideo signal information inclusive of horizontal sync signals recurringat a given line repetition rate; and wherein the distribution of saidgeometric variations along the bottom of successive convolutions of saidspiral groove is such that locations of geometric variationsrepresentative of recorded horizontal sync signals are spirally alignedin succssive convolutions of the spiral groove; and wherein said spiralalignment is such that geometric variations representative of recordedhorizontal sync signals in any given groove convolution deviate fromradial alignment with geometric variations representative of recordedhorizontal sync signals in an immediately adjacent groove convolution byan arcuate distance several times less than that occupied by half a lineinterval of recorded composite video signal information having said linerepetition rate.
 6. A record in accordance with claim 5 wherein saidarcuate distance corresponds to that occupied by one-tenth of a lineinterval of recorded composite video signal information having said linerepetition rate.